I will give you some professional advice since I do this for a living.
DO NOT take aleve advil (NSAID's--non steroidal anti-inflammatory drugs) etc on a semi-regular basis. If you read the contra-indications you will realize that use of these NSAID's even within the OTC guidelines can increase your risk of GI bleed and kidney failure. NSAID's are a major reason for dialysis and death from GI bleed--especially in people with "arthritis" who tend to take more than they realize. This can happen with no major usage or forewarning....IOW, you can take Aleve with no problems for yearsand then boom have GI bleed problems. If you are going to take NSAID's you must increase your water intake and you should eat something.
Do stretch frequently. You need to use bands etc to stretch. Also take a tennis ball and roll it up and down your back while pulling the arm across your body.
Double check all heights of tables, sewing machines hoops etc. Modify hoops etc so you are not sitting with your head hanging down.
The key to mid back pain is to sit very straight. This can mean knees down with a good arch in your lower back...this will take the stress off of your mid back. Then squeeze your shoulder blades together and push those boobies out. Your thumbs should point forward when they hang at your side if you are doing this properly. Use a Body Rite Posture aid if you have to. Do "flying" superman exercises in doorways.
Stop every ten minutes or so to pull your shoulders back and stretch. Keep an exercise ball in your sewing room and lay backwards over it, rolling back and forth. You can use the ball as a chair if you are coordinated.
If you are going to use heat, no more than 10 minutes of moist heat.